Re: Memory sharing issue by application on V4L2 based device driver with system mmu.

[daeinki <inki.dae@samsung.com>]

Michel Dänzer 쓴 글:
> On Fre, 2011-01-07 at 11:17 +0900, InKi Dae wrote: 
>> thank you for your comments.
>>
>> your second comment has no any problem as I said before, user virtual
>> addess could be translated in page unit. but the problem, as you said,
>> is that when cpu access to the memory in user mode, the memory
>> allocated by malloc, page fault occurs so we can't find pfn to user
>> virtual address. I missed that. but I think we could resolve this one.
>>
>> as before, user application allocates memory through malloc function
>> and then send it to device driver(using userptr feature). if the pfn
>> is null when device driver translated user virtual address in page
>> unit then it allocates phsical memory in page unit using some
>> interface such as alloc_page() and then mapping them. when pfn is
>> null, to check it and allocate physical memory in page unit could be
>> processed by videobuf2.
>>
>> of course, videobuf2 has no any duty considered for system mmu. so
>> videobuf2 just provides callback for 3rd party and any platform with
>> system mmu such as Samsung SoC C210 implements the function(allocating
>> physical memory and mapping it) and registers it to callback of
>> videobuf2. by doing so, I think your first comment could be cleared.
> 
> FWIW, TTM (drivers/gpu/drm/ttm, include/drm/ttm) is designed and used
> for managing memory between CPU/GPU and kernel/userspace access. I
> haven't looked at your requirements in detail, but if you haven't looked
> at TTM yet, it sounds like it might be worth a look.
> 
> 
Thank you for your advice. I would look at TTM driver.